Birch (Betula platyphylla) BES/BZR transcription factor BpBZR1-6 improves salt tolerance in transgenic Arabidopsis thaliana.

Background: Salt stress is one of the major environmental factors affecting plant growth and productivity. BRI1-EMS suppressor 1/brassinazole-resistant 1 ((BES1/BZR1) plays an important role in responding to abiotic stress in plants. Although the impacts of BES1/BZR1 on plant growth and resistance have been documented, the potential mechanisms are not fully elucidated in Betula platyphylla. This work contributes to the understanding of how BES1/BZR1 promotes stress tolerance in woody plants.

Results: Six BES1/BZR1 family members were identified from Betula platyphylla. Cis-element analysis showed that the promoters of six genes were rich in ABA-responsive element (ABRE), MYB and MBS cis-acting elements, which are reported to be involved in abiotic stress responses. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis indicated that BpBZR1-6 (BPChr10G06000) could be induced by salt stress, ABA and BRs. BpBZR1-6 was localized in the nucleus and had transactivation activity. Ectopic expression of BpBZR1-6 enhanced Arabidopsis tolerance and decreased abscisic acid (ABA) sensitivity under salt treatment. Specifically, the seed germination rate, root length, fresh weight and chlorophyll content were significantly higher in BpBZR1-6-overexpressing (OE) transgenic plants than in wild-type (WT) plants after salt stress (P < 0.05). Additionally, BpBZR1-6 overexpression showed enhanced the reactive oxygen species (ROS) scavenging capability under salt stress, including increasing the activities of antioxidant enzyme, resulting in a decrease in O₂^- and H₂O₂ accumulation, and reducing malondialdehyde (MDA) content. Meanwhile, the expression levels of six antioxidant enzyme genes were higher in OE plants than in WT plants after stress.

Conclusion: BpBZR1-6 overexpression enhanced the salt tolerance of transgenic plants by modulating antioxidant enzyme gene expression and ROS scavenging, which may provide underlying strategy for breeding of salt-tolerant plants.